Atmospheric dust is one of the key factors affecting the efficiency of solar power generation. Dust pollution will greatly reduce the power generation of photovoltaic power plants, which is estimated to be at least 5% per year. If the global installed capacity is expected to reach about 500GW in 2020, the annual power generation will be reduced due to dust. The economic loss caused by the volume will be as high as 5 billion US dollars. As the installed base of power stations continues to grow, this loss will become more serious – when the global installed capacity is about 1400GW in 2030, the economic loss caused by dust is expected to be as high as 13 billion US dollars.
01
temperature effect
At present, photovoltaic power stations mostly use silicon-based solar cell modules, which are very sensitive to temperature. With the accumulation of dust on the surface of the modules, the heat transfer resistance of the photovoltaic modules is increased, and they become the heat insulation layer on the photovoltaic modules, affecting their heat dissipation. . Studies have shown that the solar cell temperature rises by 1°C, and the output power decreases by about 0.5%. In addition, when the battery module is exposed to sunlight for a long time, the covered part heats up much faster than the uncovered part, resulting in burnt dark spots when the temperature is too high. Under normal illumination conditions, the shaded part of the panel will change from a power generation unit to a power consumption unit, and the shaded photovoltaic cell will become a load resistor that does not generate electricity, consuming the power generated by the connected battery, that is, generating heat, which is the hot spot effect. This process will aggravate the aging of the battery panel, reduce the output, and cause the components to burn out in severe cases.
02
occlusion effect
The dust adheres to the surface of the battery panel, which will block, absorb and reflect the light, the most important of which is the blocking of the light. The reflection, absorption and shading effect of dust particles on light affects the absorption of light by photovoltaic panels, thereby affecting the efficiency of photovoltaic power generation. The dust deposited on the light-receiving surface of the panel components will firstly reduce the light transmittance of the panel surface; secondly, the incident angle of some light will change, causing the light to spread unevenly in the glass cover. Studies have shown that under the same conditions, the output power of clean panel components is at least 5% higher than that of fouling modules, and the higher the amount of fouling, the greater the decline in module output performance.
03
Corrosion Effects
The surface of photovoltaic panels is mostly made of glass, and the main components of glass are silica and limestone. When wet acidic or alkaline dust is attached to the surface of the glass cover, the components of the glass cover can react with acid or alkali. As the time of the glass in an acidic or alkaline environment increases, the surface of the glass will be slowly eroded, resulting in the formation of pits and pits on the surface, resulting in diffuse reflection of light on the surface of the cover plate, and the uniformity of propagation in the glass is destroyed. , the rougher the cover plate of the photovoltaic module, the smaller the energy of the refracted light, and the actual energy reaching the surface of the photovoltaic cell decreases, resulting in a decrease in the power generation of the photovoltaic cell. And rough, sticky surfaces with adhesive residue tend to accumulate more dust than smoother surfaces. Moreover, the dust itself will also attract dust. Once the initial dust exists, it will lead to more dust accumulation and accelerate the attenuation of photovoltaic cell power generation.
04
Theoretical Analysis of Dust Cleaning
The glass surface of photovoltaic modules placed outdoors can trap and accumulate dust particles, forming a dust cover that blocks light from entering the cells. Gravity, van der Waals forces, and electrostatic field forces all contribute to dust accumulation. Dust particles not only interact strongly with the photovoltaic glass surface, but also interact with each other. To clean the dust is to remove the dust from the surface of the panel. To remove the dust on the surface of the battery board, it is necessary to overcome the adhesion between the dust and the battery board. The dust on the battery plate has a certain thickness. When cleaning it, a parallel load, a load at a certain angle (or vertical) to the battery plate, or a rotating torque can be applied to the dust layer to destroy the adhesion between the dust and the battery plate. Additive effect, thereby removing dust.
q—the load parallel to the battery plate; F—the load at a certain angle or perpendicular to the battery plate; M—the rotational moment applied to the dust layer
For the removal of dust particles, it is necessary to overcome the tangential adhesion force and the normal adhesion force of the dust particles. The normal adhesion force is the adhesion force between the dust particles and the battery plate, and the tangential adhesion force is relatively small and can generally be ignored. . If the dust is removed from the vertical direction, it is only necessary to overcome the normal adhesion force, such as cleaning with water, the process of wetting the dust particles, mainly to overcome the normal adhesion force. When the water is cleaned, the intermolecular distance is mainly increased, which reduces the van der Waals attraction and produces buoyancy, and overcomes the van der Waals force and gravity of the adhesion force of dust particles. Adding a surfactant to the water makes the effect more pronounced, and also generates a strong electrostatic force that removes dust from the panels. The tangential adhesion force must also be overcome when the dust particles move relative to the battery plate.